This invention relates to an optical recording and reproducing device which permits signals to be recorded and reproduced on an optical medium with a high density by irradiating a laser light or the like with its flux converged into a minute spot onto the optical medium and permits the signals once recorded to be erased. More particularly it relates to an optical recording and reproducing device suited to erase information at a high speed.
In such a kind of conventional devices, the light flux of the laser light or the like irradiated onto an optical recording medium provided, as disclosed in Japanese Patent Unexamined Publication No. 59-71140, has a substantially circular or elliptic shape and a "Gaussian" light intensity distribution where the light intensity is highest at its center and exponentially attenuates towards its periphery. The Gaussian light intensity distribution on the optical recording medium resulted in a Gaussian temperature distribution there, and this gave rise to several difficulties.
FIG. 1 shows a temperature distribution 28 on an optical recording medium in the conventional devices. The abscissa indicates a position of an optical recording medium, and the ordinate indicates the temperature at the position irradiated with the Gaussian light flux. In this figure, it is necessary to maintain the temperature between T.sub.1 and T.sub.2 in order to erase the signals recorded on the medium assuming that T.sub.1 is an erasable minimum temperature and T.sub.2 is an erasable maximum temperature which means a writable minimum temperature. Moreover, although the temperature for writing must be higher than T.sub.2, it should be also controlled within an implicit upper limit T.sub.3 for the protection of recording mediums.
Thus, it is troublesome and difficult to control the temperature for writing and reproduction. For example, when the information recording in a position range of X.sub.1 -X.sub.4 is intended, the temperature distribution 28 does not permit the recording in ranges of X.sub.1 -X.sub.2 and X.sub.3 -X.sub.4 whereas a possible temperature distribution 28-1 may destroy the medium because of its high temperature. On the other hand, when the information erasing is intended in the range of X.sub.1 -X.sub.4, the temperature distribution 28 does not permit the erasing in a range of X.sub.2 -X.sub.3 but leaves the information there. For these reasons, it has been proposed to individually provide laser light sources for recording and reproducing but it is still difficult to solve the above problem.